| Canopy resistance, an important parameter for calculation formula of reference crop evapotranspiration, has momentous significance for accurate calculation of reference crop evapotranspiration and diagnosing Crop-Water-Stress.With the presumed conditions of ET0 equation by FAO as a starting point, this article studies alfalfa's canopy resistance with measured data.The results show that the variation of canopy resistance increases with growth proceeding.The diurnal variation curve of canopy resistance takes the shape of “U”, whose minimum point appears at noon (lower than 50 s·m-1) and maximum point appears at 8∶00 and 18∶00 (higher than 100 s·m-1) . |